If it's only a day in just give them time.
Your new dog is also still getting used to her new environment so give her a week to get used to your house and all the new smells etc.
You don't say how old they are as they may have not established who is top dog yet.
Maybe one good scrap and then they will decide who is boss and then thing will settle down as a good pair of mutts.
Imagine if you were put in a room with someone you didn't know maybe you would be a bit guarded too judging who was going to take the lead.
So in short give them time to settle and they'll be ok