reflect type latias is reminiscent of reflect type starmie except i find it's harder to cram reflect type onto latias... i generally prefer having a utility move in fourth slot (roar is my current standby seeing as i'm a stall player). reflect type doesn't really help you sweep cause you lose your stab; sub is better if you really want to harass shit like ferrothorn. the sub also lets you get away on pursuits and only lose the substitute, rather than your entire latias. overall i find reflect type less useful on latias than on starmie. they're the only two pokes i can think of that would run it in OU.
I always found her weak even after a +2. Even after supporting her it would get revenged because of her lack of power. Any help or do I need to get better?
don't keep CMing when the opp has a counter or strong check still alive. depending on what your fourth move is, you might want to just CM on the switch to take a special attacker coming in, but subcm/roarcm etc are generally better off using their fourth move than CMing if a switch is predicted, unless the sweep is imminent. if weakened, just recover straight away on your free turns. CMing is clearly pointless and a waste of turns. don't stay in on shit like status, genesect (unless burned), etc, they all make you completely useless (if you must take status though, burn is what you want to be taking - burned latias can still sweep, just takes longer to boost up. para/toxic cannot sweep ever).
the thing is that latias IS weak even after a +2, when it's not invested in satk and has only like one attack lol. sdef steels will tank you pretty comfortably even after a few CMs and rain steels will shrug off HP fire. but your CMs also make you basically impossible to kill with any special attack, because of dat bulk. you ideally wanna burn any invested uturns, physical ice attacks, etc, and then go for the throat. until then stick to recover to stay in play and pivot. the sweep will happen when you have enough time to get to +6 - not hard if your opponent's special attacks are limited to unstabbed ice and such, but physical attackers need to be dealt with first.