Treva & the Trolls Series by Jan Brett

Treva's trouble with trolls begins when she climbs Mount Baldy with her dog Tuffi. The trolls who live there long for a dog, and they try to kidnap him. But Treva is brave and quick-thinking. She outwits one troll after another until she reaches the very top of the mountain, where five trolls are waiting--and they want her dog! From underground to mountain peak, Jan Brett's story is filled with adventure and eye-catching detail.

Christmas is Treva's favorite time of the year. But when she finds a hedgehog making off with her family's Christmas decorations and presents, she discovers two irresistible trolls who want to have Christmas, but don't understand it.