As long as the clown does not see the newly introduced shrimp as food, they will be fine. I have seen large adult clowns eat small shrimp when being put into tank. Just make sure they are larger in size.
Its a crap shoot trying to introduce another clown. Could try a tiny one and see if she will accept it as a mate. Be prepared to remove it though if she beats on it. Most of our attempts at adding a mate for a larger clown, has failed.
Although your tank is on the bottom end of size for a coral beauty, with lots of rock it may be ok. Find one thats eating mysis at least and better yet mysis & spirolina flakes. They are a tough fish and a brute also, so as long as the tomato accepts it, which again is a question mark.
With a smaller tank like that and no corals, perhaps you could remove the clown to a holding tank while adding something else and then put the clown back. Perhaps even a smaller tomato. If you could get a pair of them to live together, that would be a nice and easy to keep pair of fish for your tank. For sure I would not add any other similar sized fish then, like the angel.
Or, you could add smaller tough fish like a royal gramma or some of the other dottybacks or something like a 6-line wrasse. They both are tough and as adults, are ignorant brutes like the clown.
