Hi there and welcome to the BW
I don't think her waking up for a feed once at night is unreasonable - we had 2 night feeds at that age
. But if you think its not hunger, it might actually be schedule related which may be causing her to wake at night as I noticed that she's sleeping 2.5hrs in the morning and then nothing until 4.5hrs later (which is a long stretch for a 6mo).
I would see if the sitter can wake her from her morning nap and you then offer her an afternoon nap so that her naps are spread out a little more throughout the day. At this age the CN is hit or miss and some babies start to lose the CN. So without the CN try to aim for something like this:
6.30 - wake up
9.30-11 - morning nap
2-3.30/4 - afternoon nap
7pm - bedtime
The family coming might have been just a coincidence and also there is a large growth spurt at 4 months (as there is at 6 months) so I wouldn't be ruling out hunger just because she has slept through before. In any case, I would suggest tweaking her schedule as night wakings can also be from baby getting overtired due to not being on an age appropriate schedule.
Let me know what you think