Do yourself a favor and commit to Life Exchange. Even as a double healer and especially as a solo healer, life exchange is going to favor your team more than the slight damage output she can put out with her explosions.
Round Start buy Chronos, but as the game goes on spend the rest of your credits on Morale Boost. Ying is a character who really benefits from her ultimate, and she doesn't ever really need to hold onto her ultimate unless the round is about to end and you can use it next round. Use it as much as you can, and be sure to pop it when your flank is getting around half health or you're burst healing a tank back to full health. Then once Morale Boost is Level 3, start investing into Chronos, Haven, Veteran, or Resilience (whatever the matchup calls for)

I don't ever really invest Nimble. Her teleportation is incredible on its own with enough practice, and her Shatter healing works so far from a range that she never needs to get too close. Plus, if you need to reposition an illusion far away, you can just teleport to it and place another, then pop right back to where you were.

You may notice I put more than 5 cards but don't panic. Every Level 1 card is a viable option for your Ying deck, and whatever you choose will benefit you in some way. The cards above it are requirements though.
-Brittle is your most important card. With Life Exchange adding another second of cooldown to your Shatter healing ability, it's important to have the cooldown as low as possible. Very simple, but very effective.
-Spring Blossom is also very important, but you could go either 4-5 with this card and still see success. Your Illusions are destined to be killed by good players, but this card takes something that would be otherwise frustrating and incredibly rewarding. If your opponents are playing too aggressive to your illusions it will help you long-term placing illusions with burst healing and getting them in different locations for teleports and corner healing.
-Carry On is another very simple card, if your opponents are being too defensive then this card means the Illusions will do more healing over time and almost claim an area as your teams territory unless they destroy the illusion or let it die over time (which would give your more than enough time to replace it or place it in another position).
The rest of the cards in this set are very viable and accomplish similar goals to your win condition Ying needs to fulfil on a team. I personally really recommend Efficiency, but it's not a requirement like Brittle or Spring Blossom.