Again. Bellum = War. Bellus = Pretty/Nice.
Completely different latin roots.
Bellus originates from bonus - benulus -> bellus.
These are false friends. Just because they look similar doesn't mean that they are similar.
The point was that the plural of "bellum" is indeed "bella." 3rd declension plurals and all that.
Bella could also be used as a feminine adjective for "beautiful," but as already pointed out, it would be far more likely to be "pulchra."
...Six years of Latin, why do I mostly remember the grammar stuff? Memories of years of "why do the 4th and 5th declensions even exist? This is dumb" flooding back to me. (Yes, I know 4th declension is mostly for foreign loanwords...5th declension has no excuse)