I never understood(but never judged) ppl with mil probs until now

I've read a lot of stories on here about about ppl with mother in law problems and know ppl in person that have them. I've never judged ppl about it. Some ppl just don't click and butt heads. I've always wanted a nice close relationship with my mil (when I get one). So now I have one and though we are not close we've never had problems. There are even times my SO is on the phone with her and he tends to get a bit frustrated with her and I defend her and tell him he should be easy on her. She lives a few hours away from us with no family in her town. BUT as of yesterday, I could see now why he gets frustrated with her as I officially am too. I don't want to make this a super long post but it may end up being that way and I apologize in advance. My SO and I are currently not living in to good of and area. With me being pregnant and our lease coming to a close in October we decided not to renew and look for another place. My SO has talked to his mom in the past about moving with us so she'd be close to family and get to be more involved with her grand son when he's born. This would be her first grand child. He wants to help his mom out. Her current living situation isn't good. She's getting older. She's by herself. I'm not always all opposed to her moving with us. This would be an opportunity for us to get close and I want her to have a big part in her grandsons life. So they talked about it and she gets iffy with change and was on the fence. He gave her time to think about it and didn't push it any further but told her we would not be upset if she declined but let us know before we get to the end of September because we need to on the ball with finding places and what not. So about a week ago we didn't hear anything and assumed she didn't want to move and started looking into 2 bdrm places. Found a place we liked but didn't make any moves on it just yet when she calls and asks if the offer is still on the table because she was down. We told her the offer still there, we did find a 2 bedroom place but they also had a 3 bedroom available and we can talk to them about that. We made a plan for her to drive down to us and we would take a look at the 3 bedroom please and if she liked it would get the application and everything done that day. She agreed and we called the place and ask them to take us off of the hold list for the 2 bedroom and put us on the hold list for the 3 bedroom. So the day comes when she supposed to drive down to us and my SO call her to see if she's all set to drive down and she made plans that day so she wasn't able to drive down. He got a bit frustrated that she made plans the day she had planned to come down here but asked her if she was able to come down the next day and she said she'd let us know at which point he told her if she doesn't come down the next day he's going to have to take the offer for her to move down off the table because we are cutting short on time and need to get our stuff in order. So we left there at that and the next day comes and he calls her to which she does not pick up but messages him a really nasty text pretty much saying 'if you want me to go down there with you guys you need to come and get me and you're pressuring me to make the decision because you guys need me and if you come and get me don't expect me to co-sign for you.' First of all, nobody begged her to move down to us. The suggestion of her moving down to us was supposed to be to help her out so she can get herself in a better situation. Second of all, she was not being pressured to come down here. We asked her, specifically told her that there was no pressure, and we weren't going to get mad if she decided not to come we just needed to know before time got close. And as far as a cosigner goes, part of the reason why my SO and I are not living in a good place now is because our credit is not that great and in the process of being repaired. If his mom did live with us she would have to co-sign for us to get a better quality please but we do not need her if she decided not to come with us. My father is more than happy the co-sign for us if his mom decides not to join us. My dad has co-signed for us in the past and we were very responsible with that place and always paid on time and there wasn't a problem which is why he's willing to cosign for us again. One thing that really bothered me is that my dad is a really nice guy and people tend to take advantage of him. I hate to even ask him to co-sign for us again because I feel like I'm taking advantage of him and if it wasn't for the fact that I want my son to be in a little better of a quality place, I wouldn't have even asked my dad again. So anyway if she lived with us then we would ask her to co-sign being that she would be living there with us and we would be able to still have a good quality place because her credit is very good as well. But now she's trying to say that she basically wants my dad to co-sign for her and us to live there just because she doesn't want to. That really bothered me because like I said I cannot stand when people take advantage of my father and I feel like that's just the way to take advantage of him. And two she's been so wishy-washy about moving down with us in the first place that I would not trust us getting a place with her, having him cosign, and then her deciding halfway through that she wants to move and then leaves us with a bill were unable to pay because then that screwed us over and that screwed my dad over. Anyway super long story short we just told her not to worry about it and are continuing on with looking for places for him and I and the baby. She's now trying to say maybe she'll come up later to which he told her no because once we get a 2 bedroom there's not going to be room for her and he wants the baby to have his own room. We are not mad that she flaked, we are mad that she strung us along and delayed the process for us. I'm all for constructive criticism, but not rude opinions. If anyone has any constructive criticism or thinks may be we should cut her some slack or something, please let me know.