In my experience, it's all about acknowledgment.
Rather than say 'oh that nice dear' ( as you're busy with 100 things) say, ' oh that's great, tell me more.
If your daughter says she's feeling invisible. She's reaching out to you. Rather than say, I'm sorry YOU feel that way or I didn't realise you felt that way, say 'oh sweetheart, feeling that way must feel awful for you. That was never my intention but I want to put this right straight away.
It doesn't matter if your daughter is right, fair, or wrong. It is how she feels. Acknowledging it will go a long way. It's much better this way than to just hug and say poor you, I'll try harder.
Your daughter may have a worry or anxiety and not know how to approach you. It could be leaving the nest and suddenly feels out there all alone. ( you mentioned seeing her tomorrow)
Maybe suggest a plan for you to avoid this feeling in the future by suggesting text times, meet ups. If she's away from home, little parcels. My daughter is at uni and I send her stuff she wouldn't want to spend her money on i.e., chocolates, slippers, face masks, make up brushes etc. I enclose a card and always write a note inside saying how proud I am of her.
This isn't necessarily your fault. Sometimes we can feel in the outside. She trusts you though and do has shared this with you. That's a great sign. Hope this helps x