If her husband doesn't know then "texting" would be the least of my worries. I would be asking him to stop all contact with her entirely. Absolutely under no circumstance would I be okay with my husband engaging in any kind of romantic communication with anyone who is in a relationship with someone that doesn't know their partner is conversing in that way. There is no good reason I have ever found that cheating is a good idea and forgivable. It ends in nothing but heart ache for everyone involved and prolongs problems that should just be dealt with and tied up before anyone moves on to texting another lover.
~ "Kindness in thought leads to wisdom. Kindness in speech leads to eloquence. Kindness in action leads to love."