Baby sleep cycles are about 20-30 mins. They have a hard time connecting the cycle. Mine naps for 3 hours in a bouncer- I bounce him to sleep then at the 25 minute mark or when he starts to stir, I start bouncing again. If he’s legitimately tired, he will stay asleep. I know its not the crib but we are still working on night time sleep so I dont mind (he just turned 12 weeks). I recommend the book Precious Little Sleep and it explains sleep associations.
You say you baby wear her. Does she still wake up after 20 minutes even if you’re holding her/have her in a carrier? Some babies just don’t love being in a cot/want the closeness of a parent nearby. Also some bubs only ever catnap. My first boy didn’t nap longer than 30 minutes until he was around 7 months. My second boy was sleeping 2 hours or more from much younger. Also a lot of parents mistake bored cues for sleepy cues. When she starts crying after 30 minutes, do you try changing the activity/taking her outside/walking around the house with her? Maybe worth a try? If she stops crying and is interested then she probably was bored, rather than tired. I always followed the rule - if I have been trying to get my Bub to fall asleep for 15 minutes (generally feeding to sleep for me) and they aren’t falling asleep, then they aren’t tired enough and I’ll get them up and play with them for another 30 minutes and try again.
I think it could be her awake time and sleep pressure, maybe she is not having enough sleep pressure to sleep longer. My son is 5 months and he is awake between 2-3 hours per nap. In that wake window, we do different activities to build his sleep pressure. He does love a contact nap and will nap longer on me though. When i put him in the crib it is only 20 minutes. When your mum is in town, it’s a new person to see, explore and interact so that could wear her out meaning she will sleep longer. In the living room, is it noisy? She may like the background noise. Do you use any white noise or music when in the crib?
sorry i don’t have much idea about the sleep but just wanted to pop on to say please be careful. you said your baby is sweating cos they’re covered in blankets - overheating is really dangerous in babies!
Same with my mum and blankets. Maybe adopt the same idea just to get her off to sleep and heat check her, loosen blankets later. If mum keeps her in living room consider it, perhaps baby is reassured by the ambient noise. Naturally or years ago, babies would probably never sleep in a silent space, unless you have a white noise machine. Good luck!
My girl would sleep longer with my mom, too. Covered with blankets and happy. I wouldn't put a heating pad, tho. Might overly heat up. I added a tiny fennel or chamomile to her bottle. Sometimes, teething bothered her, so I applied baby gum gel. I apply Junior bedtime lotion on her legs before bedtime. She's 2 now. But at 1 to 5 months, she would not nap longer than 30 min. Eventually, it became 2 to 3 hrs. It will get better.