bunkins and lexie on the road to a good friendship

Bunkins the pregnant cat and lexie (my persian spayed). Lexie keeps trying to see bunkins hah runing to the room today she ran in and there was no hissing or growling they were about 4 feet from each other and just yesterday she was 10 feet away and hissed anyhow to my question should I enforce lexie not geting into the room? or should i show them to each other off and on I think they are becoming more and more tolerent with each other and may one day be friends. also both cats have calmed down I am able to approach bunkins without hearing a MMMMMMMMEEEEEEEEEEEEOOOOOOOOOOOWWWWWWWW in a low pitch and even hold her after she has seen lexie and she has been purring too. what do you think?