Hello, Leah,
I’m sorry to hear your mother is unwell at this time. I hope for a speedy recovery and for you both to enjoy a visit to "the world of yesterday, tomorrow and fantasy" sooner than later.
Yes, in most cases, it is OK to cancel existing
theme park reservations and rebook new reservations for other dates. Your
theme park tickets will remain linked to your Disneyland Resort account after
canceling your reservations. To book new reservations, visit the "
My Theme Park Reservations" page and select new dates for which your park tickets are still valid.
If standard park tickets are wholly unused and expire before you get a chance to use them, you can
apply the value of the tickets toward the cost of new tickets of equal or greater value. This can be done by visiting a main entrance ticket booth or reaching out to a Cast Member with the
Tickets phone line or via chat online or in the
Disneyland mobile app.
Again, I wish the best for your mom as she recovers. May you both share many magical memories together at The Happiest Place on Earth soon.
~Tony