@ToTeras and Kirito Rick - There is one farm event healer named Juno/Yuno who should be coming in the next one or two waves. Her skill let's her deal magic attack through, so she is more of a damage-dealing healer rather than the normal healer.
@namhoang909 - There is a bug with the blizzard maps in that they reduce range of all units by 50% rather than the usual 30%. Screwed me over too. I heard that the only common healer that can reach your units is CC55 Alissa with her extended range at level 55. If you have Fedora at a good level and skill level, you can use her. I think Chydis might be able to as well, but I'm not sure about that one. AW Saria or AW Marr might be able to reach your units too since their AW passive gives them additional range. The unit I used to surpass that bug was Rinne with her skill extending her range.