Learn Spanish (Latin America): Ella es una amiga leal y honesta.

No, the rule is based on the sound of the next word. You only change y to e when the following word starts with an "ee" sound (words starting with i- or hi-, like hijo). Since honesta starts with an "o" sound (the 'h' is silent!), the y doesn't change.

Why doesn't the adjective leal have a feminine ending to match amiga?

It does match, it just doesn't change its spelling! Adjectives that end in a consonant (like -l in leal) use the exact same form for both masculine and feminine nouns. The second adjective, honesta, changes to end in -a because its base dictionary form ends in -o (honesto).

Why are both adjectives placed after the noun here?

In Spanish, descriptive adjectives generally come directly after the noun they describe. When you have two descriptive adjectives describing the same noun, you usually put them both after the noun and connect them with y (and), just like in this sentence.

Is the 'h' in honesta pronounced?