because we're afraid that you may have tampered with them.

If there is a certain kind/size you like best, you can bring your own and ask her if you can use them, but it's definitely a case of YMMV and she may very well say no.

Also, don't ask her ahead of time - that would be the equivalent of talking about sexual services which is a big no-go.

... The provider will be more comfortable using ones she brought. Yes, their are some crazy guys out there so reliable reputable ladies will want to use their own.  

However you having some with you isn't a bad idea. Keep them in the original box still sealed. If for some reason she didn't have any or you ran out during the session then you'd be set. No matter how well planned things are sometimes crap happens.

3-pack in case she runs out.

You should know there are certain scams & having condoms on hand can deflect them.

It's nice to consider carrying backups...
but carrying backup condoms could get you in trouble if you're monogamous with an SO on birth control.
It's not worth that risk to me to carry them.
The provider assumes this responsibility.  
Kind of like who's supposed to get the engagement ring/ wedding rings.  
In a decade I've never seen a provider who wasn't packing.  

The exception is if you have fit issues but you'll have to weigh that risk