Need help with introducing cat to dog

I have a friend who "inherited" a cat when her brother passed away. The cat
is female, spayed, about 7 years old. My friend has never had a cat before;
she currently has a 15 year old dachshund. My friend is trying to introduce
the cat and the dog but is having some difficulty. She is keeping the cat
separated from the dog and bringing them together under supervised
conditions. But the dog, even though she is 15, becomes quite excited when
she sees the cat which scares the cat. I told my friend that it is going to
take time to acclimate the dog to the cat, but my friend is becoming quite
discouraged and is thinking of taking the cat to a shelter.

Does anyone have any ideas or suggestions on how to make this introduction
go smoother? Thanks.

S.