First off, let me just say that I really like Yareli and her abilities, the only thing I have a gripe with is the lack of synergy (and that Merulina isn't an exalted K-drive), so let me off some ideas that not only could make her abilities synergize better but potentially even alter the Helminth landscape slightly.
Sea Snares and Riptide don't just do cold damage but can also proc the cold status effect. This would make her a bit more of a crowd control frame while also making my next suggestion work.
Aquablades does increased damage to enemies that are afflicted by the cold status effect. This not only makes it that the blades synergize with Sea Snares and Riptide, but also means it can synergize with subsumed abilities that proc the cold status, which could make people interested in trying out this abilities (like Thermal Sunder) on Yareli but also makes Aquablades more appealing on frames that have abilities that create cold status procs. It would also make weapons that deal the cold status a bit more powerful/useful.
Aside from that, the only other thing that I think would make Yareli truly better would be making Merulina into an exalted k-drive. Sure you could allow ranged mods to increase Aquablades range, however I actually feel like doing so would actually do more harm to the ability then people actually believe (after all the blades deal damage to enemies that touch the blades, not enemies within a radius determined by the blades.
So there's my penny for my time.
Have a good day.