Paris with 11yo DD

[pastimperfect]

I'm hoping to take my DD to Paris over the Easter holidays - prob just a 2 day/3 night thing. We're likely to go by Eurostar.

Can anyone recommend:

a) good (and inexpensive!) places to take her - Eiffel Tower, Arc de Triomphe on the list, but are there any gems in Paris that an 11 yo would love to see?

b) a good place to stay (not cheap, but also inexpensive )

c) any good places to eat?

many thanks

Tickets for the Eiffel Tower sell out ages in advance, so book early.
Musee d'Orsay is nice if you like art.
Cite des Sciences et Industrie is fantastic if you're at all sciency.