IANAM, but...
1) "15 Elemental Fire" will not trigger a Spell Shield. "I call forth a Flame Bolt!" will not trigger an Elemental Shield. Since effects are theoretically supposed to have only one delivery now (since 9th came out), there can be no attack which would be applicable to both a Spell Shield and an Elemental Shield, since both work against a delivery. Thus, no conflict. The same goes for any other delivery -- Poison for example.
2) Reflect Magic and Spell Shield both specifically state that you can only have one OR the other on at once, not both.
That said, there *are* some confusing cases where the "one delivery" rule comes close to breaking down, but these are generally specifically answered for each effect. For instance, Spellstrikes -- it's a weapon strike, but specifically counts only as a spell.
What gets tricky is when something hits you and you have *both* a defense vs the DELIVERY and a defense vs the EFFECT. For instance, say you have a Resist Element, a Bane vs Fire, and a a Spell Shield and you're hit with a Flame Bolt. Theoretically, any of those 3 defenses would work -- two work vs the EFFECT while one works vs the DELIVERY. Bane specifically allows you to use it before other defenses, but Resist Element does not. So when you're mixing effect and delivery defenses, you really need to know the specifics of the defenses.
Hope this helps.
-Bryan