Senna, whose mother is the great Ayrton Senna's sister, went on to race for Renault (now Lotus) last year and for 2012 has switched to Williams.
"What matters is that the team can give Bruno the best conditions to develop his ability," Viviane Senna told TV Globo.
"I was not happy with Hispania. They had no spare parts, so if something was broken it would be patched up for the next race. You never knew when the next thing was going to break.
"Yes, that was a risky team," she admitted.
Many observers see 2012 as 28-year-old Senna's last chance to prove he is even a shadow of his late, great uncle.
Viviane insisted: "People remember Ayrton the winner, the champion, but few remember how long he took to get there.
"Bruno went from nothing to F1 in five years. It's an unfair comparison to those who have done it (racing) for their whole lives."