Don't feel guilty, you have no reason to. You are not replacing Izzy in any way - she and you both know that. You are thinking of Jasmine and what is best for her, and also finding a way which will help heal your heart a little easier and bring some joy into your life, and there is nothing dishonourable about that.
It is the opposite; putting your own emotions slightly to one side in order to make sure Jasmine is happy, you are proving what a considerate and wonderful piggie owner you are, and by allowing yourself to love another piggie it will be a great comfort to Izzy that you'll have some happiness and something to focus on to help ease the pain slightly from her passing.
I adopted pigs days after the deaths of very much loved ones also. I have/had various grouping situations but none of them was quite right after the loss of each pig, so I brought in new pigs to help the current pigs and try and create a better grouping situation for them all.
I lost Charlie in March 08, and three days later I adopted two young girls and gave one of them the second name of Charleyrose. I lost two girls recently (a week apart in Dec 08 and Jan 09) and gave the two girls I adopted (two days after the death of the last girl) second names of Lottie-Rose and Tuppyrose. I find incorporating the names to be a great honour to those recently lost.
I advise having a second name as tribute rather than first, as there will only be one Izzy, and you want to keep awareness that the new pig is an individual in their own right even though they came into your life in the honour and remembrance of another pig.
The simple fact that you are willing to open your heart to another pig, to continue your piggie adventure, is a beautiful tribute to Izzy's life. By continuing to give piggies a loving home and continuing to learn and develop your piggie skills, you are doing Izzy proud.