Yes you can exchange with her Sundays, or ask her to take her annual leave. BUT, no matter what you do, must be that BOTH you and she agree to the arrangement, and remember to write it down and ask her to sign!
Did you guys talk about holiday arrangement before signing the contract? If not, unless she now agrees to your proposal of dedcuting her Sunday leaves and annual leaves, it may not be a right act.
If she agrees now, good for you. If she disagrees, don't push it - afterall, you didn't mention about the deduction of her Sunday leaves and annual leaves when you go travel.