I didn't know she was in heat, what do I do? My husband was given a female mini dachshund for his birthday as he had them when he was younger and he has always loved them.
Now I don't know what to do since she and my male chihuahua just tied about 35 minutes ago.

You can take her to the vet and get the 'morning after' pill for dogs. Then you should get her spayed to avoid this from happening again.

Agree, go and get a misalignment injection (can be done within 48 hours of a mating) or just book her in for an emergency spay.
If you can get her booked in within the next few days there will be a minimal extra charge and you won't ever have to worry about it again.

If you intend on keeping the puppies (if she is pregnant) then we can offer you advice, but the above methods would be the preffered options in this scenario.