For what it is worth, I think it may be your hormones/in your head somewhat. It may just be a normal lull of you both being busy that happens in every friendship occasionally. You said she asked if you would come over to visit, but you were busy that day. It happens! Life is busy.
I don't ask pregnant people how they are feeling regularly. Especially, not in the first trimester/early on. I may when they are super close to their due date. I don't know I think I just think being sick is part of being pregnant and being pregnant is a choice. I ask people who have a serious illness or getting over being sick how they are feeling. I understand that people can be very sick during pregnancy, but I don't know I just again feel like it is part of it.
I also just don't have much tolerance for people whining about being sick during pregnancy, so I may have a different view. I have seen many people (not saying you have) complaining that having to puke daily and other symptoms are the worse things they have ever been through and how will they get through it... well, they will. I am "tainted" by my past pregnancy where I went through the worst (stillbirth) so being sick from pregnancy doesn't register at all on my things I should complain about. I don't judge others for complaining, but I will not open those threads.
Again, extreme case obviously, but I also didn't whine about being sick even before going through my loss because it is just part of it. I also never really expected anyone to ask how I was feeling, so it may just be a difference in personalities.
Anyway, I wanted to just give a different perspective. Hopefully, you can take it for what it is. I'm not judging or trying to be harsh at all. I agree with others to try to open a dialogue to talk about what's bothering you with her. I know if something is bothering me I'll make it a bigger deal in my mind as time goes on. It will probably be as simple as I'm sorry I've been busy and haven't thought about it!
Hugs to you and hopefully it gets resolved quickly so you can have your friendship back at full.