Charger bank and cable.
Perhaps a nice handcream - maybe L'Occitane's lavender one to help relaxing if it is stressful visitng and not knowing about needing to stay?
Or a pillow spray (Neals'Yard is one company that does it, and I know I;ve seen others).
A travel washbag (the clear ones with a zip you can get for airports) holding various minis -
Shampoo, conditioner
Nice shower gel (L'Occitane or Molton Browne?)
Deodorant
Facial wipes and moisturiser
Mini hair spray or gel or moulding mud?
Perhaps a face mask or eyemask?
I know one company (and I cant remember the name offhand sorry) does eyemasks in individual pouches in boxes of 4 or 8 - plain or lavender ones - so she could pop one in the bag and replenish when home again
And there are lots of different face masks in individual pouches now - could be nice to use if she needs to stay and be up late while they are settling or similar
Hairbrush
Pack of grips or bobbins if she has long hair that might need tying up
Hairband to keep it out of her face?
Shower cap (in case she doesn't have time to wash/dry hair)
There's something called "No Blow Dry" which is good for wet hair when you can't dry it - holds it in relatively ok shape
Pen, pencil, notebook (with tearable pages might be good for lists etc) and puzzle book (little sudoku or similar book to while away time)
Small hot water bottle or wheat bag
Hat and gloves and scarf and umbrella
Spare underwear and socks
Comfortable but practical PJs
Favourite tea bags (maybe fruit teas or similar for relaxing as well) or sachets of coffee or hot chocolate?
Portion packs of favourite biscuits or long-life snacks (might be useful to have breakfast bars etc for following morning travel back to work etc?)
Purse with change for parking meters, hospital vending machines, work vending machine for important coffee etc
Travel mug? To be able to have a hot tea in bed at night, or coffee on the road in the morning etc?
Refillable water bottle (and possibly something like Robinson's ultra small bottles of very concentrated squash to squeeze into it)
Small fleece blanket or comfy fleece jacket or cost cardigan to throw over whatever she;s been wearing for the day or to travel in early mornings/late nights
Loyalty card/gift card for a coffee shop local to her DPs house?
Nail file and plain (colourless) varnish and a tub of remover wipes
Spare tights in her usual colour
Small sewing kit
A book of short stories that might grab her attention and make her laugh when she needs to but won't need a lot of concentration
Sorry, a bit random there