...Canon R5 with 100-500...would be beyond your 2k budget. I would look at a mirrorless...
DP Review liked the Nikon Z5 as an entry-level fx mirrorless...
If she wants to stay with a dslr, a used Nikon D850 would be the best way, imo.
Problem with the Canon or mirrorless is that none of her lenses will work.