"Low on 155 ammo" - who says? and in what context (low at the front, low in country, what?), low on regular 155 rounds or the high precision stuff? The Ukrainians don't have big stockpiles of ammo just sitting around waiting for a Russian missile strike, it's widely dispersed.
Launch a GLCM at Crimea? yeah that would be a good idea. First they aren't operational now and the only GLCMs the US built were armed with nucs, so can you imagine what the Russians would think if a GLCM was launched at them? Could the US re enable ground launched Tomahawks? Maybe, but I'll bet that would take a looong time to prepare, train and deploy.
The US position is no long range offensive weapons for the Ukrainians, so no cruise missiles, no long range ballistic missiles (ATACMS).