Ex on the beach, friend or foe?

I am married to my man who was in a previous relationship for 10 years with an awesome girl. At first I was threatened and told my man he was not allowed any contact, 4 years into this relationship, I thought this was how life was, and the 1 dog that his ex has was horribly sick (they were their dogs together and he loves them dearly) she took them 2 years into our relationship because she got a farm, and great Danes are an expense we just couldn't. So she called him to let him know that the dog was going to the vet and it looked bad, and in this situation I wanted him to go see his doggy, but I wanted to be there, ( exes fiance out of town on business) so the following day we went through and met up with the ex, and I waited with her for my SO, and then we got the bad news where doggy had to go :(. I felt horrible for her as she balled her eyes, and my SO tried to be strong, and I also having the dog for 2 years, also choking up, and afterwards, she invited us back to her place to see the farm, we chatted, and got on so well, and I've messaged her since to check how she was coping, and then decided to open the friendship door, she was so happy to be friends, swapping stories, I can't wait to start this new friendship aswell, she's just a girl who has no filter and can't determine boundaries, but means no harm and always looks out for others above herself. Have you befriended an ex of SO?