Pretty much every NPC you speak to on your way to the Githyanki tell you the Githyanki are violent sadists. Even Lae'zel. While I can see the argument that you trust Lae'zel to handle the diplomacy it isn't completely out of left field that these Githyanki, who have been killing innocent people around the coast according to Zorru, might be violent and that you should plan for a fight if things go south.
It is also obvious from a lore perspective. Githyanki have a "kill on sight" rule about mind flayers and their tadpoles. This is only complicated by Lae'zel insisting they have a cure that almost definitely doesn't exist. In fact if you talk to her as a Githyanki your character says they have never heard of this protocol.
At the same time though new players won't necessarily know the lore well enough to know the Githyanki reputation. I do think adding a few more obvious hints that you're walking into a tense situation could be set up. Maybe have Lae'zel be a little more obviously unsure of herself, since most players are going by what she says for their understanding of the Gith. Maybe have Shadowheart, the NPC who hates Gith, provide a strong and clear counter-example of what the Gith are like. If you have both at camp have her chime into your dialogue time with Lae'zel doubting her and making snide comments about how violent Githyanki are, which Lae'zel then reinforces because she as a Gith sees being blood thirsty and remorseless as GOOD things.
I think that'd go a long way to making sure the PC knows there's a very high chance of a fight and to plan accordingly.
