Hard to search on, does Improved Spell Sharing work with Spell-Like Abilities? Improved Share Spells has specific text that precludes them, but Improved Spell Sharing lacks that text.
My understanding is that it works RAW, but with all the FAQs treating SLAs as not spells, I thought I'd check to see if anything's been said.
I can't find anything addressing the issue, but I see no reason to think that it would work with SLAs. I don't believe "you can use a SLA wherever you can use a spell unless it says otherwise" is RAW or RAI. Rather, places where you can substitute a SLA for a spell are specifically called out. The extra text in Improved Share Spells is there because the author foresaw people raising the question and decided to head them off at the pass.
Usually, a spell-like ability works just like the spell of that name. A spell-like ability has no verbal, somatic, or material component, nor does it require a focus. The user activates it mentally. Armor never affects a spell-like ability’s use, even if the ability resembles an arcane spell with a somatic component.
A spell-like ability has a casting time of 1 standard action unless noted otherwise in the ability or spell description. In all other ways, a spell-like ability functions just like a spell.
This is why there are so many faqs making distinctions between spells and spell-like abilities. The Core Rulebook treated them the same except where explicitly different RAW, and for years SLAs were spells for all kinds of cases like caster levels and prerequisites. Then an about face was made. I don't disagree with the decision (I always thought SLA's as early access into prestige classes was gimmicky), but since they haven't changed the Core text, it's unclear what RAI is.
The issue with SLA is the FAQ saying that Augment summoning works for SLA summoning. Augment summoning only works for spells, so SLA are spell enough to work with that. But yes, recently it seems that the nature of SLA has changed some, so it's hard to know if things that apply to spells apply to SLA when applicable.
Personally I rule that they are unless otherwise mentioned they aren't. Thus they would work with this feat.