I do think you're a great mum, that you love Summer and Summer loves you.
You've admitted that you're depressed and I think that you need to speak to someone about that, it will make things seem a lot worse at the moment. Also your hormones are all over the place with being pg, well I know mine are and at times I'm regretting getting pg so quickly as I am finding it hard to cope with Ella and dealing with the tiredness, so you're not alone.
I don't think your mum should take Summer, I think you need to work through your PND and get away from your mum and set up home with Chris (it sounds like you want that). Not trying to suggest your mum doesn't see Summer but she needs to be more supportive of the way you are feeling and not try and take your daughter away from you whilst you are down.
Ella will sit happily over my mums for hours, yet get frustrated with me at home within minutes, she just likes the change of scenery and chattering to new people. I know that doesn't mean she loves me any less though.
You're doing a great job Kayleigh, admitting what you have on here is a big step