Please tell me this gets better?

We are all having a difficult time the now. My two year old (turned in Oct) is having a really difficult time adjusting to her new baby sister. Since Hannah was born my husband had managed to get time off work, and my MIL so it was great having them here at home to occupy my two year old while I tried to get to grips with the newborn phase again and breastfeeding (this time around). But when it is just me and the two girls, that’s a different story. My two year old cries continually for 90% of the time, she won’t play with her toys, she has started falling onto floor pretending she’s fallen and then saying that she is sore. She started crying hysterically at her nursery yesterday (a nursery she loves and asked to go to!) and I had to go and pick her up as they believed she was unwell. Walking around saying her legs are sore. When I go to get her she was absolutely hysterical, definitely seemed as though something was wrong. Concerned I contacted my husband to come back from work as I may need to get her to see a doctor. Low and be hole as soon as my husband walked into house her whole presentation changed. She was shouting daddy daddy daddy all happy. Told him she wasn’t sore and that she was fine, and proceeded to take him through to bedroom to play. Obviously he was annoyed he’d taken the time off work for this when she actually had nothing wrong with her. I’ve tried including her in caring for her sister, changing nappy’s, bathing etc, picking her clothes, but it doesn’t seem to make any difference. She demands my full and undivided attention when I am on my own with her but she can’t wrap her head around fact that her baby sister is also there and very much needing me at the minute with the breastfeeding. She hasn’t been horrible or nasty to her sister which is a blessing, but she is obviously subconsciously presenting like this because she’s upset and the new dynamic of things. I’m just so upset. I feel like a terrible person and a terrible mum as it’s difficult not to feel resentment when my toddler acts this way but obviously I understand she did not ask for this, she never asked for a sister and her whole little life has been turned upside down. Any advice please? 😓😢