7 month old issues??

Okay so I’m going to list some things out and give some background so bare with me please!!!

I watch a 7 month old girl a few times a week. I have been since January. She’ll be 8 months on May 8th. I also have my own kiddo that’s 10 months old, and I know they say not to compare babies because they all develop differently... BUT I have some genuine concerns that I’m just trying to get some insight on

So, her parents don’t really do a whole lot of floor time and I guess hold her quite a bit at home (mom has said both of these directly to me.) Obviously when she’s with me I literally don’t have that option. When mom leaves she’ll usually sit her on the floor with me and my son to play and then she’ll head out without making a scene. Well , she absolutely hates the floor and usually starts getting very upset within a few minutes.

She doesn’t really play with toys when she’s here, no matter how I much I try to engage with her and the toys and play all together.

She doesn’t stay very long on her tummy. I try to do it as much as possible her since she doesn’t get very much of it at home. She will get pretty upset if she’s on her tummy more than a few minutes. When she is doing tummy time, she always has her arms straight out, either in front of her or beside her. I have never seen her support any of her weight using her arms or make any attempt at any kind of progress towards crawling. And I mean what so ever.

She also is oddly stiff sometimes when I am holding her. Like her legs and arms, idk she just seems so like stiff?! Idk if that will make sense to anyone.

Another thing to that really concerns me is her sleep. She would usually go down about 10-10:15. Mom says to not let her sleep passed three hours whenever she falls asleep. I keep a sound monitor in with her when she’s sleeping so I can hear her and there’s so many times where she’ll just be like mad chillin in there. Like she’d rather be in there by herself than playing or being social or anything. Once I go get her out, she acts ready to go back on within an hour or so. I’ve never had her up longer than two hours between her naps. And it’s not that I’m not trying to. She will literally scream and cry. And as soon as she’s in the crib with it dark she chills out.

And she’s usually pretty emotionless. Except when she’s upset obviously. I’ll get some smiles out of her but it’s not often.

I don’t know. Maybe I’m overthinking and being dramatic. It’s just so hard because I care for her too but have some honest concerns. I’ve never addressed them to mom because I don’t even know what to say and I don’t want to come across like I’m mom shaming or judging or anything like that. And I’m not trying to compare, but like my son was crawling before 8 months old.. and even pulling or scooting everywhere since a little before 6 months. Idk idk idk.

If there’s any insight on anything, I’d appreciate it. I just don’t even know like what to think.