I work with a group of developers in a company having about 1000 employees. 
A transgender person who identifies herself as a woman has joined our team. 

* She gets upset when we use masculine pronouns (such as "he") to address her, which we obviously do out of habit. 
* She also insists on using the ladies toilet, which makes our female coworker uncomfortable. 

Taking this to HR is extremely delicate, as they might think we just don't like LGBT people. While we don't want to discriminate against a transgender person, her needs cause issues for us. 

How should we handle this situation?