User blog comment:FeaturedMe/Feat's Anime Review - Episode 148/@comment-4933386-20120918053910/@comment-5782519-20120919230758

The reason for it is because by the time they fought Angel originally to the time Gray fought Angel after, she had already used up a lot of her life form. There was no doubt Angel was stronger than Dan and Gray, however her endurance was already at its limits. After all, she is the only person to actually destroy Dan's shield and armour, something none of Team Natsu could do. As for Gray, she was chucking him around with only a 30-yen coin summon (which wasn't using that massive attack it used before, either).