Stuff for her room that fits her preferred aesthetic - if you can give us a vague sense of how she styles herself / her stuff, can give more specific suggestions. I will list a few things but these are quite general and could be off-base! Happy to add more if you could share a bit more info 
Room -
Hanging wall decor like a moon phase decoration, tapestry, small decorative mirror (Urban Outfitters)
Cuddle cushion (UO also has these but can get cheaper elsewhere - different colours and fabrics available for more girly or neutral style)
Candles - scented or the fashionable Holm styles (twisted or bubble), but doesn't have to be that brand
Typo's website has nice noodle bowls, mugs, etc.
If she has a particular interest in an aesthetic like cottagecore or dark academia, etc, then room decor to go with that style would probably be very well received. Etsy is often the best place! I can help you find stuff.
Books - the big, hardback fashion books (Catwalk, the complete collections) are popular on Tiktok, so definitely worth considering if she's into style. Also big hardback travel books from the Assouline series. Since she's 18, a really nice, chic recipe book or cocktail book could be nice.
Makeup - Charlotte Tilbury, Glossier, Laura Mercier powder, Natasha Denona
Beauty and skincare - Glossier skin stuff, Mario Badescu sprays, Rituals, Pixi
Olaplex and Ouai hair products, satin pillowcase and scrunchie if hair is long. Silk pillowcase if you want to go upmarket!
Does she enjoy fitness?