The way I see it, Harec, beats Doldren. Doldren beats Shae and Shae beats Harec. As Tekato states, you just don't know before hand.
A high level Alicia is everyones nightmare with some levels ideal for her jump, special ability. This badly needs a cooldown.
You're probably, from your description being hit by Shae's second rare - Sa-Dhu. It's a beast, but Shae is one of my mains and unless you have a fast reload card, you'll have problems.
With every mission with an antag you have to play as a team. The minute they appear, team together and take them out. When you do, use their respawn cooldown to complete mission objectives. Like Alicia, some missions are tailor made for Shae. Because of this, added with dreadful matchmaking, there are alot of maps I'll completely avoid. The 'Mouse and the Snake' mission will always pull in Alicia and Shae antagonists.