"Grander" is a comparative adjective, meaning it compares two things in terms of grandeur. The word itself doesn't have a gender, and it can be used to describe things that are traditionally considered masculine, feminine, or neither.
Here's why there isn't a feminine form:
* English doesn't usually create feminine forms of adjectives: While some languages do this, English generally doesn't.
* "Grander" doesn't describe gender: It describes a quality or degree of grandeur, not a person's gender.
If you're trying to describe a feminine version of something that's "grander", you could use other adjectives like:
* More magnificent
* More impressive
* More elegant
* More stately
For example, instead of saying "the grander palace", you could say "the more magnificent palace".