Answer:
she is angry and thinks he is teasing her
Step-by-step explanation:
Puck has mistakenly applied the juice from flower "love-in-idleness" (wild pansy) on Lysander’s eyes. When applied to the sleeping person, the juice makes them fall in love with the first person they see.
Helena is the one to stumble upon Lysander and wakes him up. As Helena is the first person he saw, Lysander falls in love with her immediately.
But Helena knows Lysander loves Hermia and is very confused by his sudden change of heart. Helena gets angry and thinks he is mocking her (Wherefore was I to this keen mockery born? / When at your hands did I deserve this scorn? ). She scolds him for playing with her and insulting her (I thought you lord of more true gentleness. / O, that a lady, of one man refused. /Should of another therefore be abused!). Offended and embarrassed, Helena runs away.