plenty of ways. dodge her e, it's really narrow and has a cast animation to read it by.

have your support play more aggressive. until level 3 shes very underwhelming. putting her low by then will drastically reduce her lane presence.

soraka causes her problems

odds are, you can out dps her. leona deals bursts, but after ewq she literally does nothing for 10 seconds. ignore her and jump on her carry.

If she's camping a bush, ward the damn bush (dodge or bait her to fail her zenith if necessary).

If she's not level 3+, make her rectum bleed, don't just let her sit in the brush collecting XP for free.

If you can make her initiation failhard (Ezreal, Corki, maybe Tristana?) then do it and lol while she rages because she's kinda mana hungry if she doesn't get her massive kill bursts.

Try to make her initiate where here ADC can't get in range to proc her passive, if her ADC isn't proccing her passive on her every skill, the damage from a Leona initiation goes waaaaaaaay down, but especially beware of Corki and Ezreal here, they have, again, blinks and spammy as heck skills that will let them proc her passive every time it gets on you after they blink in from well out of range, so try to mess with them and apply pressure while the blink is on CD.

Edit: Oh, yes, Soraka does mean things to her between actually providing lane sustain and shutting down her initiation comboes hard. Taric can also do nasty things to her, but that requires a lot better timing and coordination. Janna can take a dump on her upturned face, but Janna is really hard to play right even without that, so, Taric timing X 2 basically.