General overview

April occupies a unique niche as a helidrop sniper. You can drop her anywhere without worrying about baiting aggro, and her redeployment time gets a heavy reduction from her talent. However, this means that she's a very poor replacement for a core sniper, so she should be an accessory investment and not part of your primary teambuilding.

E2? Not mandatory, but if you intend on using her a lot she really benefits from further development. She gets a shorter redeployment cooldown, becomes cheaper, and gets a lot out of masteries.

Talents

April's talent reduces her redeploy time by 15 seconds at E1 and 20 seconds at E2. At E2, she also gets -1 DP cost.

Skills

S2 is April's bread and butter skill. After she's deployed, she gets Camouflage and a hefty ATK buff for 20 seconds, which is often more than enough time for her to do what she needs to do.

Masteries

S2 is the only skill you will want to put masteries on. The gains on it are linear with each mastery level, so you may as well go all the way to M3, which will get you an extra +30% ATK multiplier and 6 seconds of duration.

Modules

Module Y gives April +8 ASPD when there are ground enemies in range. The base upgrade is useful because more ASPD means she can kill things faster, but you should go to at least mod2 for her talent upgrade, which reduces her redeploy time by 25 seconds and her DP cost by 2. Mod3 reduces her redeploy time by 28 seconds, which is nice, but not as significant as mod2.