Excel online is pretty bad if you compare it in terms of features.

lacks advanced features (tried it)

I love FOSS but LibreCalc sucks! Word is good, I did a project with it, I am pretty sure you can get the hang of it. Not sure about anything else tho

Can she use Google sheet? You can download the sheet as Excel file.

actually the whole purpose of using excel is because of the advanced features. Doubt if you will find it on web version of Gsheets.