How to reply when she says she's been dealing with a family illness lately

The apology and the explanation are the actual message here. She has been slow to reply, short with you, or absent, and she wants you to know the reason is not that she lost interest. Read it as a request to be understood, not a request for help. The fact that she mentioned it at all, instead of just going dark, tells you she trusts you a little already.

How heavy it sounds matters. Something like "it's been a lot, my mum's been unwell" is a light disclosure, and she is probably fine with a short warm reply. Something with more detail about hospitals or appointments means she is in the thick of it and may be tired and emotionally stretched. Match the weight she gives it without going heavier than she has. If she has used one sentence, a short reply is the right size.

Replies in this situation fall into a few kinds. One is the plain acknowledgement: it names what she said, says you are sorry it is hard, and asks nothing. It tells her you heard her and are not making it awkward. A draft is this kind if it could be read by someone who knows nothing about the dating context and still makes sense as kindness. It should leave out any question about the illness, any advice, and any link back to the two of you.

Another kind is the light re-entry: it acknowledges, then lets a bit of normal life back in, like a question about something unrelated she has mentioned before or a small remark about your day. It works when she seems to want some distance from the heaviness. A draft is this kind if the second half would still make sense if the first half were deleted. Leave out anything that asks her to perform cheerfulness.

A third kind is the open offer: a short line saying you are around if she wants to talk or if she just needs to vent, with no pressure to do so. This suits a woman who seems isolated with the situation. A draft is this kind if it ends the message without a question she has to answer. Leave out any plan or promise you may not keep.

After you reply, leave it. She is dealing with something that takes time and energy, so a lag of a day or two on her end is normal and not a sign anything is wrong. Do not send a second message asking how things are going unless she gives you an opening, because that puts her in the position of having to report back.

A gentle check-in a few days later is fine, as long as it is short and does not ask for an update on the illness. Something that simply shows you are still thinking of her works better than a question she has to answer. If she replies warmly, you can gradually return to normal conversation. If she goes quiet for a long stretch, it is reasonable to send one more kind message and then let it rest. Continuing to message after she has stopped replying reads as pressure, and stopping entirely after a heavy disclosure can feel abrupt. One follow-up, then wait for her.