Pay taxes for n a Roth conversion

I hope I am more clear on my question this time. We are thinking about doing a Roth conversion on my wife’s 457b. We don’t have any cash on hand to pay the tax. Instead of having the tax withheld on the conversion. I am wondering if it makes sense to pay the tax from a different account that I have and it is a Roth account. If we did a $100,000 rollover and had to pay federal tax of $20,000 would it make sense to take the $20,000 for the tax from my Roth account. That way my wife would get the full $100,000 into her Roth side of her 457b. Is this a silly idea ? I absolutely love ❤️ listening to you and Jon on Wednesdays. Thank you Terry.