Sister may have had a slight heart attack, do I text her?
It's never wrong to err on the side of kindness and besides, I have found with relatives that it blows them away when you give them the impression that you had no idea that they were even shunning you. It sort of spoils it for them when you seem perplexed as to notion that anything unusual in your relationship was happening. They like it when they know their efforts are bothering you so there's nothing worse for them than finding out that the person they were ignoring, didn't even notice.
Being an older person, it may seem more heartfelt to your Sister if your were to send an "old school" greeting card with a short hand written note, rather than sending a text message which may seem a bit modern and cold or might seem to imply the need for an immediate response from her, in kind.
A card with a nice poem or message and a brief note in your own handwriting that she can read while she is recuperating, will seem more personal. You could include a photo or two of you and your daughter and put your return mailing address on the top left side of the envelope as you usually would but you could also include your phone number in that location rather than in the card, so it won't seem as if you are expecting her to contact you but it's there if she ever want's to.
(It's amazing what lengths one has to go through just to contact a JW relative)