Used cradle matress?

lmj8284

I know it's a no no to get a used crib matress and we will be purchasing a new one. 

However, we have a cradle that our daughter will sleep in for the first few months that my dad hand built.  My sister used it for her 2 babies and had to buy a custom made matress b/c of the size.  She has had a cover on it the whole time.  What are your thoughts on using the same matress in the cradle that she's had in there? 

If it was from a stranger I would definitely buy a new matress.  But it's only been used by my nieces and it's always had a cover on it so I'm thinking it's okay to keep it.