I have multiple builds depending on the situation, and Surprise!- I use ALL of her talents. My go-to talent I use is life link, 2nd is goddess' blessing, then sacrifice. People are skeptical on using sacrifice as they see it as just a 2nd life in exchange for a lot of healing capabilities, but they don't seem to realize that it's better to have your healer still in the fight than have her huge healing in the respawn room. I use life link for 2-2-1 team comps, goddess' blessing for off-tank/tank-less comps, and sacrifice for flank-based enemy comps. Sky walker is always present as it gives Io a subtle but powerful distance boost when leaping.

Life Link Build:

My life link build is meant to give a lot of leeway to redeploy, so that I can juggle burst healing tanks and bringing Luna back to me for a strong defense. Since I can't rely on my shots the entire time, it's safer to get guaranteed moonlight restoration from Luna than to look for enemies to poke, so I prefer protectors > moonlight garden.

It also allows me to keep healing up on tanks when I need to have Luna. This build is pretty standard if you wanna make Io's presence a known threat but a hard to knock down target. Flanks will have to think twice before engaging, and your crescent card gives you a guaranteed Spacer.

Goddess' Blessing Build:

This build reduces Io's healing capacity but maximizes her buffs when she heals. Teammates will now receive 1350 Heals/s and also 40% speed boost and 25% dmg reduct. This can set up a lot of flank supporting play styles and help teammates get out of sticky situations.

Luna can still be used as a reliable defensive tool and you won't have to worry about using her to heal. Io can play very aggressively and can secure kills with flankers. I also use Luna as a damage sponge on some occasions because Luna can also chip/point cap. This can buy your team lots of time to set up plays.

Sacrifice Build:

This is the most hardest to pull off talent Io can use. Sometimes flankers are a pain to deal with so in this build I use Luna as a frequently moving bodyguard, stunning incoming flankers or use her as a sentry point. I do play really safe when placing her as she's my only ticket to a 2nd life. Luna basically turns into an "I win" button. She can deny attempts to secure a kill on you and keep a flank on watch. You can outplay duels with the 2nd life in most cases so that's a nice touch.

Be careful using this build however, because when you aren't getting an Evie off your a** or pressuring you should be healing.

Items:

Offensive and Utility Cards are what help Io change the tide of a fight. If the team doesn't have a burst healer, I start off with Nimble rather than caut or etc, since it's gonna make you harder to hit and can traverse around the map a little quicker. I don't prioritize morale boost since you can get it up quickly, but it's always an option.

Chronos is useless since you already have a reset card for Luna.

If you aren't playing life link, save a slot for kill to heal.

Offense items can vary, but the safest choice is cauterize. I get tier 2 before going for other items most of the time, an exception when there's a non-burst enemy healer.

Bulldozer 3 can deal 1000dmg/s and wrecker deals 1300dmg/s.

When I go for a secondary offense item, I go for deft hands - Let Me Explain.

Io needs to be constantly doing something, or else she won't be useful. I'd rather spend 250-750 credits to save some few moments patching up Luna for a big fight, saving my teammate, or defending myself than to be stuck reloading. Io's reload is 1.6 seconds, so cutting it down to nearly a second can give time to summon Luna or quickly heal a teammate. However, I rarely get tier 3.

Deft hands 1/2/3 = 1.28/.98/.64 seconds